Sprinkler head corrosion protector



' June 16, 1959 R- M. PFALZGRAFF ET AL SPRINKLER HEAD CORROSIONPROTECTOR Filed Nov. 14, 1955 Unite 890,758 SPRINKLER HEAD CORROSIONPROTECTOR Application November 14, 1955, Serial No. 546,333

11 Claims. (Cl. 169-37) This invention relates to automatic fireextinguishing apparatus, and more particularly to an improved protectivecap for automatic sprinkler heads installed under conditions ofmechanical stress and chemical corrosion.

Although the prior art shows many varieties of protective caps forautomatic sprinkler heads, at least some of which are intended toprotect the temperature sensitive element against corrosive action ofvarious ftunes, many tests and experiments with all known types ofprotective devices failed to solve the problem where the sprinkler headsare installed in ducts carrying exhaust fumes under velocities reachingto 100-150 miles per hour and where the fumes comprise mixtures of oneor more of the following materials: sulphur dioxide, hydrogen sulphide,sulphuric acid, sodium sulfate, other sulphur compounds, and moisture.

These ducts are customarily fabricated of a synthetic plastic materialcapable of withstanding the above noted conditions, or from a metalwhich is coated with such corrosion resistant synthetic material. Thenecessity for'this coating has introduced a serious fire hazard and nopreviously known automatic fire extinguisher could be used in theseducts.

Glass caps or protectors were not satisfactory because the seal betweenthe cap and the housing could not be made sufficiently tight so thatthere would be assurance that it would be broken off in the event of afire. If the cap is retained by an external temperature responsive linkor element, this element soon becomes eaten away or so corroded that iteither fails prematurely or will not rupture when it should. Experimentsproved that various types of paper with or without a coating areineffective because the penetration of the fumes apparently takes placeby a process of osmosis and any coating or covering for the papersufliciently strong to withstand the air pressure and at the same timeprotect the sprinkler head against the corrosive action of the fumes,will not burn or otherwise fail in the event of fire. Where a greasetype seal was used for a glass cap, it was found that the fumes eitherseeped through the grease or in some cases hardened the grease to suchan extent that the cap could not be forced off by the water pressure.

Two additional problems were encountered as a result of our work. It wasfound that if the cap contained any sort of a seam or joint, the seamfailed first, thus permitting the sprinkler head to open. The cap,however, did not fall away from the sprinkler head and, as a result, thespray pattern was completely destroyed. In addition, it was found thateven using a cap formed of nitrocellulose material, if the cap shape wassuch that only part of the cap was removed upon the application ofelevated temperature, the remaining part also destroyed the spraypattern, thus eliminating the effectiveness of the sprinkler head.Peculiarly enough, the very properties of nitrocellulose "which areemployed to enhance the present invention may operate to defeat thepurpose thereof unless the cap is constructed in accordance with thepresent invention. For example it has been found that if the nitro-States Patent 1 improved protective cap for automatic sprinkler headscellulose cap is made of relatively small diameter so that it closelyfits the sprinkler head, the heat generated when.

the bottom of the cap ignites, very quickly sets off the sprinkler andthis action is so fast that only a small portion of the cap around thetip has an opportunity to burn before the sprinkler valve opens and putsout the fire on the remainder of the cap. This very effective and fastop eration of the head proved to be a disadvantage because the unburnedportion of the cap destroyed the spray pattern and in effect acted as ashield to direct all the water directly downward in a highly localizedarea. course is very undesirable from the standpoint of eflicientoperation of an automatic sprinkler system. Our experiments indicatedthat a synthetic plastic capof nitrocellulose or similar material couldbe made sufficiently strong to withstand the pressure and corrosionpresent in such ducts, and further, when properly designed, these capscan be made to operate satisfactorily under the most severe conditions.

Therefore, in one embodiment of the invention, it is proposed to use arelatively small diameter cap of nitrocellulose or other syntheticmaterial in which the wall of the cap, well above the path of the spraypattern, is formed with portions of reduced thickness, as by scoring.The bottom of the cap is Weighted with lead or similar material so thatthe cap, upon being subjected to an elevated temperature, always partsat the portions of reduced thickness, with the lead weight completelyremoving all portions of the cap which might otherwise interfere withthe spray pattern. Another embodiment of the invention eliminates theneed of cap scoring and weight simply by increasing the diameter of thecapto provide a desired inside clearance between the cap and thesprinkler head. With this construction, if the bottom portion of the capstarts to burn, the fire will not immediately actuate the sprinkler headand thus there is suflicient time for the cap to burn away around theedges before the sprinkler valve opens. This has been found effective inremoving all portions of the cap which would otherwise interfere withthe spray pattern after the sprinkler has been set off. It has beenfound as a practical matter that it is desirable, if not necessary, touse a weight with any material except nitrocellulose. A furtheradvantage of this material resides in the fact that the heat released bythe burning of the nitrocellulose cap is sufficient in itself toaccelerate I the opening of the sprinkler head. It will be noted thatthe characteristics of nitrocellulose which are considered to bedisadvantageous in conventional sprinkler head cap structures, asmentioned above, are taken advantage of in the present invention andcontribute in providing a more eflicient device. A relatively large capof nitrocellulose which is molded or drawn was found to completely solvethe problem and it is believed that we are the first to mold thismaterial in comparable shapes and sizes.

The primary object of the invention therefore, is to provide an improvedprotective cap for automatic sprinkler heads.

A further object of the invention is to provide a protective cap forautomatic sprinkler heads capable of withstanding the elfects ofcorrosive fumes for an extended period of time.

A further object of the invention is to provide a pro- 7 tective cap andinstallation for sprinkler heads capable of withstanding pressuresincident to extremely high fluid velocities.

A still further object of the invention is to provide an improvedprotective cap for automatic sprinkler heads which will not destroy thespray pattern of the sprinkler when the cap is partially burned away.

A still further object of the invention is to provide an Patented June16, 1959 This of.

3. having. means for removing a large portion of the cap under elevatedtemperature conditions.

A further object of the invention is to provide a protectivei cap for:automatic sprinklerheads so constructed"- that the: capxwill.substantially burn away beforethe Fig. 2 is a vertical section showing.a modified form:

of our improved protective cap, and.

Fig. 3 is a transverse section through an exhaust duct showing themanner in which the improvedsprinkler head assembly is mounted.

The invention comprises essentially the provision of a drawn syntheticplastic cap securely. mounted and covering the individual sprinkler headnozzle. The preferred form of cap is hemispherical in shape and providessubstantial clearance between the sprinkler head and the inside of thecap. Another embodiment uses a cylindrical cap more closely fitting thesprinkler head and provided with portions of reduced thickness, as byscoring, and a weight which together cooperate to completely remove thelower portion of the cap when the portions. of reduced thickness giveway under elevated temperature conditions. The material found to behighly satisfactory for making such caps is a nitrocellulosecomposition;

Referring now more particularly to the drawings, a plurality ofsprinkler heads 5, 5 are mounted in the upper ceiling structure 6 of anexhaust duct "assembly 7 or in any other suitable location where anautomatic sprinkler system is to be used. The sprinkler heads areconnected tothe main 8, and are secured thereto by means of a brassfitting 9, lock nut 10, and nipple 11. Each sprinkler 5 is provided withthe usual thermally responsive element and a deflector 12 which is sodesigned to direct the water in the most effective spray pattern. Inexhaust ducts of the type referred to above, the metal duct structure 6ais lined with a synthetic plastic coating indicated at variousplaces bythe letter C. This coating is desirably a sheet of. plasticizedpolyvinyl chloride. The preferred form of protector cap 15 is generallyhemispherical in shape and is' provided with an integral annular flange16 which can be bolted between the upper plate 6 and an annular plate orcollar 17. This method of attachment is found to provide a seal aroundthe rim of the protective cap thus preventing the admission of anycorrosive fumes to the inside of the cap. By making the radius of thecap shown in Fig. l on the order of 4 to 5 inches, it has been foundthat ample clearance between the heat responsive element in thesprinkler head and the cap itself can be provided and maintained. Thisdimension has been found to be critical when used with the standardsprinkler head which extends 3 inches below the ceiling. Preferably thecap itself is made of nitrocellulose which is-highly flammable and aquick burning material. When the bottom of the cap 15 ignites, it hasbeen found that the sprinkler head will not open until the cap hasburned away to a point Well above the path of the spray asit leavesdeflector 12.

The modified cap 20 shown in Fig. 2. is substantially cylindrical inshape and has a rounded lower end. Likewise this cap may have ahorizontal annular flange 21' which is securely sealed and clamped totheceiling structure 6 by means of bolts 22, 22 and nuts 23, 23. Due tothe fact that there is much less clearance between clear the spraypattern. by installing a weighting element 25 of lead or other heavymaterial in the bottom of the cap 20. To make sure that the entire lowerportion is removed, the cap is scored or otherwise formed with reducedthickness portions at 26, 26 well above any possible path of the spraypattern. This feature is essential in using a nitrocellulose materialfor the cover unless the form of Fig.

the sprinkler head 5 and the cap 20, it has been found 1 is employed, inwhich case the scoring and the weights can be eliminated.

The thickness of the cap may be made to withstand any stress imposedupon it by external forces such as the fluid velocity in the duct. Theshape of the caps and particularly that of Fig. 1 lendsitself readily toa pressure molding or drawing operation. Furthermore, it is possible tocompletely and effectively seal the cap so that corrosive fumes ormaterials cannot penetrate to the sprinkler head.

While the invention has been described as being of particular importancewhere sprinkler heads are used in exhaust fume ducts, it must be alsonoted that other applications are indicated; for example, in woodencooling towers which very often have liquids containing highly corrosivematerials running thereover.

Having thus described our invention, we claim:

1. A combination including a supporting structure, a'sprinkler headmounted on said supporting structure, a unitary sprinkler headprotective cap cooperating with said supporting structure to completelyencompass said sprinkler head, and means for securing said cap to saidsupporting structure, said cap beingformed of thermoplastic material andincluding a seamless portion extending in spaced relation with andenclosing said sprin kler head and an integral annular flange engaged bysaid securing means.

2. The combination as defined in claim 1 wherein said cap furtherincludes means for effecting the removal of a section of said enclosingportion of said cap under elevated temperature conditions.

3. The combination as defined in claim 1 wherein said seamless enclosingportion of said cap is hemispherical in shape.

4. A unitary protector cap for heat responsive sprinkler heads, said capbeing formed of thermoplastic material and including a seamlesssprinkler head enclosing portion having an open end, and a securingflange formed integrally with said seamless portion and extending alongthe open end thereof.

5. A protector cap as defined in claim 4 wherein said cap furtherincludes means for effecting removal of a section of said sprinkler headenclosing portion under elevated temperature conditions.

6. A protector cap as defined in claim 4 wherein said seamless enclosingportion of said cap is hemispherical in shape.

7. A seamless protector cap for automatic sprinkler heads and the likeformed of synthetic thermoplastic material, said cap having an annularflange extending along an edge thereof and forming the base of the cap,and a weight disposed within said cap for completely removing a portionof the cap remote from its base when the cap is subjected to elevatedtemperature conditions.

8. A combination including a supporting structure, a sprinkler headmounted on said supporting structure, a sprinkler head protective capcooperating with said supporting structure to completely encompass saidsprinkler head, and means for securing said cap to said supportingstructure, said cap being formed of thermoplastic material and includinga seamless portion extending in spaced relation with and enclosing saidsprinkler head, an integral annular flange engaged by said securingmeans, and a weight disposed within said cap for completely removing aportion of the cap'remote from saidflangeunder elevated temperatureconditions.

9. A protective cap in accordance with claim- Tin This disadvantage isovercomewhich the cap is formed with portions of reduced thickness whichare located between said annular flange and weight.

10. The combination of claim 8 in which the cap is formed with portionsof reduced thickness which are 10- 5 cated between said annular flangeand weight.

11. The combination of claim 10 wherein said sprink=ler head includes aspray deflector and wherein said cap portions of reduced thickness aredisposed substantially above said deflector.

References Cited in the file of this patent UNITED STATES PATENTSGrinnell Mar. 12, 1889 Glenck Mar. 3, 1908 Haller Dec. 12, 1916 EstyJune 19, 1917 Ramsey Feb. 17, 1920 Jenkins Aug. 3, 1920

